Hydrogenation of carbohydrates



HYDROGENATION F CARBOHYDRATES Leo Kasehagen, West Chester, Pa., assignor to Atlas Powder Company, Wilmington, Del., a corporation of Delaware No Drawing. Filed Dec-4, 1958, Ser. No. 778,057

6 Claims. (Cl. 260-635) This invention relates to the process of hydrogenating carbohydrates and more particularly to the process of hydrogenating saccharidic compositions containing substantial proportions of reducing sugar groups and poly-saction to glucose, substantial quantities of poly-saccharides normally formed in the hydrolysis of starch.

Still further objects will become apparent in the detailed description of the invention set forth below.

In accordance with the present invention monomeric sugar alcohol compositions containing very low contents of residual sugar or of material hydrolyzable to sugar are produced from saccharidic compositions containing reducing sugars and poly-saccharides hydrolyzable to reducing monosaccharides by first hydrogenating the said composition in substantially neutral solution under hydrogen pressure, in the presenceof a hydrogenating catalyst .and at moderately elevated temperature until the reducible groups are substantially all reacted; then adding a strong mineral acid in controlled amounts and subjecting the acidified solution-catalyst mixture to hydrogen pressure at a higher temperature whereby hydrolysis of the polysaccharidic material ensues and the resulting monosaccharides are hydrogenated substantially as rapidly as they are formed. The concurrent hydrolysis and hydrogenation reactions are continued until the content of material hydrolyzable to mono-saccharide is decreased to the desired low value and the resulting monosaccharide hydrogenated to polyhydric alcohol.

For convenience in the present specification reference will be made to reducing sugar content and total sugar content of the products and process solutions of the invention. Percent reducing sugar is the percent of apparent dextrose determined by the copper reduction method standard in the sugar analysis art and corresponds to the available reducing groups in the sample. Percent total sugar is the percent of apparent dextrose obtained by copper reduction analysis of a sample which has first been subjected to acid hydrolysis in dilute solution, and

corresponds to the sum of the available and potential reducing groups in the sample. In practicing the invention hydrate material is thus converted to the monomeric sugar alcohols obtainable by hydrogenating any mono-saccharides present in the carbohydrate and mono-sacchates atent O rides derivable by acid hydrolysis of polysaccharides con tained therein.

The process of the invention is particularly useful in the production of hexitols from starch hydrolysates and the following more detailed description will be based on its application thereto. It is to be understood, however, that the invention is not limited to the processing of starch hydrolysates but includes within its scope the treatment of any carbohydrate mixture comprising a reducible saccharide and poly-saccharides hydrolyzable to reducing monosaccharides.

The present process is applicable to raw materials coniprising saccharidic compositions containing reducing groups and polysaccharides which are hydrolyzable to reducing monosaccharides. Of the total reducing groups (available plus potential) a minimum of about 40% should be in the available form in raw materials employed in the process of the invention, i.e., the ratio of available to potential reducing groups should be at least about 2 to 3. Thus the process is applicable to reducing disaccharides such as maltose or lactose which contain one available and one potential reducing group per sugar molecule. Also suitable as raw materials are acid hydrolyzed starch products wherein the extent of hydrolysis is such that the dextrose equivalent of the product is at least 40. Corn syrups of 40 to 60 dextrose equivalent, containing glucose, maltose and higher polymers of glucose are readily available commercially and may be utilized in the practice of the invention. Preferably raw materials are starch hydrolysates of dextrose equivalent or higher such as the 70 sugar or 80 sugar of commerce.

An aqueous solution of the saccharidic material to be processed in accordance with the invention is prepared and, if necessary, adjusted to substantial neutrality, i.e., to a pH of from 6 to 8. The pH adjustment may be effected by the addition of small amounts of alkaline or acidic material as required or by treatment of the solution with an ion-exchange resin all as well understood in the art. The said aqueous solution may contain from 25% to 75% by weight of sacchardic material although it is generally preferred to employ solutions of from 40% to 60% concentration.

The neutral solution is then subjected to hydrogenation in the presence of a catalyst at a temperature of from C. to 160 C., preferably from C. to C. under a hydrogen pressure of from 1,000 to 3,000 pounds per square inch, preferably from 1,000 to 2,000 pounds per square inch, until substantially all of the available reducing groupshave been hydrogenated. The catalyst employed may be any conventional hydrogenation catalyst such, for example, as the reduced metal hydrogenating catalysts taught in US. Patent No. 1,963,999. A particularly preferred catalyst is reduced nickel supported on a diatomaceous earth.

To the resulting solution, there is added a. small proportion, from 0.05% to 1.0% by Weight based on the weight of original saccharides, of a strong mineral acid. Phosphoric acid has been found particularly suitable for the purposes of the invention although other acids, such as hydrochloric or sulfuric acid, may be employed. The acid may be forced into the reacting vessel without reducing the temperature. and pressure or, alternatively, the pressure may be released after cooling'the reaction mixture below its boiling'point at atmospheric pressure and the vessel opened to add the acid. In either event, the acidified reaction mixture isnext'heated to a temperature of from 200 C. to"220 C. under a pressure of from 1,000 to 3,000 pounds per square inch and the reaction continued under these conditions until the total sugar content, i.e., the sum of the potential and available reducing groups calculated as dextrose, is decreased to the the reducing sugar content to 0.04% (dry basis).

' ducing groups.

desired value, in any event to a value of less than 0.7% (dry basis).

The contents of the pressure vessel are then discharged, the aqueous solution separated from the suspended catalyst and the dissolved monomeric sugar alcohols recoveredin conventional manner.

' The following specific examples are presented to illustrate the process and show the treatment of specific saccharidic compositions in accordance with the invention.

Example I The raw material was a commercially available 80 corn sugar with a dextrose equivalent of 90.8. Into a 3 liter rocking autoclave there were charged a solution of 209.4 grams of the sugar in 290.6 grams of water and sufficient 'of a reduced nickel catalyst supported on a diatomaceous 'earth to furnish 2% nickel on the carbohydrate solids. :The contents of the autoclave were put under 1,000 pounds per square inch of hydrogen pressure and heated 'to 140 C. for 60 minutes. By this treatment the reducible carbonyl groups were substantially all converted to carbinol. 0.4% by weight (based on the sugar taken) of phosphoric acid was then introduced into the autoclave,

'in the form of an approximately 2% aqueous solution, the temperature raised to 200 C. and hydrogenation continued for 75 minutes at 1,000 pounds per square inch. j'Ihe pH of the solution after addition of the acid was 3.4.

total sugar content was 0.38% (dry basis).

Example II The raw material was a high conversion starch hydrolyzate with a dextrose equivalent of 90.8. A solution containing 269 grams of hydrolyzate solids in 231 grams of water, having a pH of 6.6, and 20.2 grams of a supported reduced nickel catalyst (containing 21.1% Ni) were charged into a. 3 liter rocking autoclave, pressured to 1,500 pounds per square inch with hydrogen and heated to 160 C. for an hour. The pressure at temperature was approximately 2,000 pounds per square inch. The pH of the solution fell to 5.7 during this treatment and The autoclave was cooled to room temperature and 1.0 gram of 85% phosphoric acid was added to the contents, lowering the pH of the solution to 2.0. Hydrogen was introduced to a pressure of 1,500 pounds per square inch and-the temperature taken to 200 C. and held at that temperature for 2 hours. The pressure at reaction temperature was 2,510 pounds per square inch. The final pH of the solution was 4.6. Upon cooling, filtering and recovery of the monomeric polyhydric alcohol in the usual Way a product containing 0.04% (dry basis)reducing sugar and 0.44% (dry basis) total sugar was obtained.

Example III The raw material employed was the crude corn sugar from an un-neutralized starch hydrolysis batch. The dextrose equivalent was 90 and the pH (in approximately 50%-concentration) 1.1. A solution of the crude corn sugar was brought to substantial neutrality by passage through a bed of anion exchange resin and adjusted to 41.9% solids content (by weight). 500 grams of the solution together with an iron-promoted nickel catalyst supported on a diatomaceous earth (2% nickel on sugarsolids) were introduced into a 3 liter rocking autoclave and pressured with hydrogen to 1,500 pounds per square inch. The temperature was taken to 150 C. for one hour to hydrogenate substantially all of the available re- The autoclave was cooled, the pressure released, and 0.5% (based on the sugar originally taken) of H PO introduced. The hydrogen pressure was again raised to 1,500 pounds per square inch and the autoclave heated to 210 C. for 1.5 hours. After cooling, the autoclave contents were discharged and the catalyst filtered from the reduced solution. The hydrolysis and hydrogenation were very complete as evidenced by sugar analysis. The reducing sugar content was 0.05 (dry basis) and the total sugar content was 0.08%.

The foregoing examples illustrate application of the principle of the invention to the batch-wise hydrogenation of carbohydrates. The invention is equally applicable to continuous hydrogenation processes as illustrated in the following example.

Example IV The apparatus employed comprised 3 vertical tubular reactors with provision for conducting a slurry of sugar solution and catalyst together with an excess of hydrogen under pressure in upward direction through each in series. Reference is made to US. Patent No. 2,642,462 for a more detailed description of the autoclave system. Provision was made for the injection, in metered amounts of a dilute phosphoric acid solution into the bottom of second reactor. The following reaction conditions were established.

When a steady state had been reached, samples of the final product and of the reaction mixture leaving each of the first and second reactors were collected over a period of seven hours, separated from suspended catalyst and composited for sugar analysis. The analytical results are tabulated below, all sugar contents being reported on the basis of dry solids content of the solutions.

Percent; Percent Reducing Total Sugar Sugar Feed Solution '91. 08 Product from 1st Reactor. 0.39 8. 50 Product from 2nd Reactor 0. 15 0. 86 Final Product 0. 13 0. 20

It is evident that the bulk of the available reducing groups were hydrogenated in the first reactor. In the second reactor, approximately 90% of the potential reducing groups were liberated by hydrolysis and hydrogenated as rapidly as liberated. The third reactor served as a clean-up for hydrolysis and reduction of the remaining total sugar to yield a product of satisfactorily low reducing and total sugar contents.

What is claimed is:

1. The process which comprises catalytically hydrogenating a saccharidic composition containing both reducing sugars and polysaccharides hydrolyzable to reducing monosaccharides wherein the ratio of available to potential reducing groups is at least about 2 to 3 in substantially neutral solution under hydrogen pressure of from 1000 to 3000 pounds per square inch; and at a temperature of from 125 C. to 160 C. until the bulk of the available reducing groups are hydrogenated, adding from 0.05% to 1.0% by weight, based on the weight of original saccharides, of a strong mineral acid, and subjecting the acidified solution-catalyst mixture to hydrogen pressure of from 1000 to 3000 pounds per square inch at a temperature of from 200 C. to 220 C. whereby hydrolysis of the said polysaccharide ensues and the resulting monosaccharide is hydrogenated substantially as rapidly as it is formed, continuing the concurrent hydrolysis and hydrogenation until the total sugar content is less than 0.7%, and separating the catalyst from the resulting monomeric polyhydric alcohol solution.

2. The process of producing a monomeric polyhydric alcohol from a starch hydrolyzate of at least about 40 dextrose equivalent which comprises hydrogenating a substantially neutral solution of the said hydrolyzate in the presence of a finely divided solid hydrogenating catalyst under a hydrogen pressure of 1000 to 3000 pounds per square inch at a temperature of from 125 C. to 160 C. until the available reducing groups are substantially all hydrogenated, introducing from 0.05% to 1.0%, based on the Weight of starch hydrolyzate solids, of a strong mineral acid and subjecting the acidified mixture to a pressure of from 1000 to 3000 pounds per square inch at a temperature of from 200 C. to 220 C. until the total sugar content is less than 0.7%, and separating the hydrogenating catalyst from the resulting monomeric polyhydric alcohol solution.

3. The process of claim 2 wherein the said strong mineral acid is phosphoric acid.

4. The process of claim 3 wherein the said starch hydrolyzate has a dextrose equivalent of at least 80.

5. The process of claim 3 wherein the said hydrogenation catalyst is finely divided nickel supported on diatomaceous earth.

6. The process of producing sorbitol from a starch hydrolyzate of about 90 dextrose equivalent which comprises preparing a substantially neutral solution of said hydrolyzate containing from to solids, introducing into said solution sufficient of a finely divided nickel catalyst supported on diatomaceous earth to provide a nickel to hydrolyzate solid ratio of about 2%, subjecting the solution-catalyst slurry under agitation to a temperature of C. to C. under hydrogen pressure of from 1000 to 3000 pounds per square inch until the available reducing groups are substantially all hydrogenated, injecting about 0.5% by weight, based on the hydrolyzate solids, of phosphoric acid, raising the temperature to 200 C.-220 C., continuing the hydrogenation at 1000 to 3000 pounds hydrogen pressure until the total sugar content is less than about 0.7%, and filtering the supported nickel catalyst from the resulting sorbitol solution.

References Cited in the file of this patent UNITED STATES PATENTS 2,280,975 Power Apr. 28, 1942 2,546,103 Lolkema et al. Mar. 20, 1951 2,759,024 Kasehagen et a1 Aug. 14. 1956 

1. THE PROCESS WHICH COMPRISES CATALYTICALLY HYDROGENATING A SACCHARIDIC COMPOSITION CONTAINING BOTH REDUCING SUGARS AND POLYSACCHARIDES HYDROLYZABLE TO REDUCING MONOSACCHARIDES WHEREIN THE RATIO OF AVAILABLE TO POTENTIAL REDUCING GROUPS IS A LEAST ABOUT 2 TO 3 IN SUBSTANTIALLY NEUTRAL SOLUTION UNDER HYDROGEN PRESSURE OF FROM 1000 TO 3000 POUNDS PER SQUARE INCH, AND AT A TEMPERATURE OF FROM 125*C. TO 160*C. UNTIL THE BULK OF THE AVAILABLE REDUCING GROUPS ARE HYDROGENATED, ADDING FROM 0.05% TO 1.0% BY WEIGHT, BASED ON THE WEIGHT OF ORIGINAL SACCHARIDES, OF A STRONG MINERAL ACID, AND SUBJECTING THE ACIDIFIED SOLUTION-CATALYST MIXTURE TO HYDROGEN PRESSURE OF FROM 1000 TO 3000 POUNDS PER SQUARE INCH AT A TEMPERATURE OF FROM 200*C. TO 220*C. WHEREBY HYDROLYSIS OF THE SAID POLYSACCHARIDE ENSUES AND THE RESULTING MONOSACCHARIDE IS HYDROGENATED SUBSTANTIALLY AS RAPIDLY AS IT IS FORMED, CONTINUING THE CONCURRENT HYDROLYSIS AND HYDROGENATION UNTIL THE TOTAL SUGAR CONTENT IS LESS AND 0.7%, AND SEPARATING THE CATALYST FROM THE RESULTING MONOMERIC POLYHYDRIC ALCOHOL SOLUTION. 